The aim of this project is to investigate nitroxides as potential MRI (Magnetic Resonance Imaging) contrast agents for delineating early cartilage degeneration.The depletion of the cartilage proteoglycans (PG) is an early event in the joi nt destruction seen in rheumatoid and osteoarthritis. MRI is very sensitive in the delineation of cartilage, however, the MR signal of cartilage is almost completely determined by the amount of collagen in the cartilage and it has been demonstrated that depletion of PGs does not produce changes on conventional MR images. We are using rabbits to test whether intra-articular injection of positively charged nitroxides as paramagnetic contrast agents can specifically delineate PGs within cartilage. Preliminary results indicate good stability of nitroxides in the knee and preferential accumulation of nitroxides in the cartilage. In t he next phase we will induce reversible cartilage degeneration to test the efficiency of our approach.